I just got a ton of sphacelatum seedlings and came looking for info too. OMG, what did I do!?
That is a HUGE plant! I'd love to hear what works, and what doesn't.
I was going to suggest wiring it up bare root and hanging it under a tree. I don't know how bro-in-law will feel about the wire. What about a hammock?
I just got a ampliatum in a trade and was told they are high-light, rugged plants, and like to be neglected. I sometimes find it hard to initiate good root growth on a smaller division with minimal roots when mounted. You may want to nurse it a little in a pot - then mount it when you have new roots.